Harnessing Sustainable Biofuel with Extremophile Microbes

Sandia’s Rajat Sapra examines assays
for the screening of engineered enzymes.
(Photo: Sandia National Labs)

Rugged microbes equipped with a unique set of survival skills find high-temperature and acidic conditions a welcome home. And scientists have a peculiar fondness for these “extremophiles,” freaks of nature that live outside the boundaries of normal existence. These are bugs that can grow in the harshest of conditions, from sulphuric acid to high-salt environments.

Part of the reason scientists are interested is extremophiles potential to be put to work to produce next-generation cellulosic-based biofuels.

How? These microbes can perform feats that bioengineers till now only dreamed of. They offer, perhaps, the best hope to tear down rigid plant material without using specialized chemicals or high amounts of energy and, perhaps, one day to create new fuels to power autos and trucks. Scientists and engineers at Sandia National Labs are taking the lead in the effort.

“We are looking at extremophiles that can thrive in high temperature and acidic conditions,” said Rajat Sapra, staff scientist and engineer with Sandia National Labs.

“Bugs that can grow in sulphuric acid are of great importance because nature has already done all of the genetic customization and adaption. It saves scientists trying to create superbugs with these modified capabilities.”

Over the course of the next few years, Sandia scientists are planning on working with the three different parts of the cellulosic biofuel process, which include deconstruction technologies for breaking down cellulosic materials and engineering extremophiles for pretreatment processes.

“What we look at in terms of processes is trying to streamline these extremophiles. If you look at stonewashed jeans, that process is achieved through the use of a bacterial extremophile,” says Sapra.

The world of biofuels and cellulosic ethanol comes down to a pretty simple equation. Cellulosic sugars are based on six carbon sugars, which is common among plants. The longer the length of the carbon chains, the more energy density is stored inside the plant material. The researchers explain energy density with a simple equation of one gallon of ethanol having the same energy density as 0.6 gallons of gasoline.

Trouble is all of that energy density is locked up pretty snugly in the cellulose and lignin materials of plant, which means you have to pay an energy or chemical cost to break it down to get at the rich density of energy. It isn’t the challenge of converting sugars to ethanol, it is how to break down the plant material into a mulch that can then provide sugars.

Sometimes missing from the big discussions about biofuel processing is the energy cost of getting the foodstuffs to the place where the fuel is going to be refined. It doesn’t make a lot of sense, for example, to transport large volumes of poplar trees from one region to another by truck.

That’s why scientists like Sapra are clear about the real Achilles’ heel for making biofuels economic and scalable. It comes down to looking at the entire process as an integrated one. And the key focus is taking into account the enormous scale of the process.

At the end of the day, the real answer for sustainable, economically viable biofuels resides in grasses and woody plants, instead of food crops. Agricultural waste is a starting point. Growing and extracting for corn stover and rice straw is all about converting waste plant material that would otherwise be burned into a high-energy-density material from which ethanol can be processed and refined.

There are three basic steps in biofuel production:

  1. Take the biomass and break it down.
  2. Deconstruct the material into polymers.
  3. Convert the sugars into fuels.

Researchers and engineers are focused on the goal of taking the entire conversion of biomass material into sugars and ethanol and doing it in one large vat or container. This is called consolidated bioprocessing and has obvious advantages over other approaches in both economics and efficiency.

Even though second-generation biofuels are still years off, the ability to harness the mysterious ways by which nature has solved extremophiles’ problems of survival is surely going to be a boon to efficient fuel production.

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